Hello all.

Can anyone post the formula for figuring out lathe spindle rpm's?

I just got a 1940's wood lathe (belt driven) rebuilt and running. On the motor shaft is a 4 part pulley with different diameters from large to small. On the opposing lathe shaft is a 4 part pulley with different diameters from small to large. The smallest motor pulley opposes the largest lathe shaft pulley. The motor turns at 1750 rpm.

What is the proper formula to plug in the different pulley sizes?

Thanks for the help.

Rog

All you need do is form a ratio between the motor shaft pulley and headstock pulley. If the motor headstock pulley is twice as large as the motor shaft pulley that's 2:1 or 1/2 of 1750.

The size of the motor shaft pulley itself isn't important - it's going to be turning at 1750 rpm regardless. It's how much larger, or smaller, the pulley it's running with that matters. In other words, the ratio between the two.

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Motor Pulley Pitch Diameter X Motor RPM = Headstock Pulley Pitch Diameter X Headstock RPM

If the motor is turning 1750 - why not turn the motor by hand a few turns and count the lathe shaft turns, then multiply.



Edited 1 time(s). Last edit at 05/14/2008 10:17PM by Chuck Mills.

Motor RPM x Motor pulley diameter / headstock pulley diameter to get ratio

e.g


Motor RPM = 1750, motor pulley A dia. = 2.0", Headstock Pulley dia - 4.0" -----
1750 X 2 / 4 = headstock RPM is 875rpm

move to a large motor pulley and small headstock thus

1750 X 3.5 / 1.5 = 4083 rpm

You use the same type of formula to predict gearing changes on a motorcycle when changing sprockets.

cheers,
Owen

Thanks for the help guys.

Rog